1. Field of the Invention
The present invention concerns air flow paths through air conditioning units. In particular, the herein described invention pertains to the flow of air through the indoor section of a rooftop type air conditioning unit.
2. Prior Art
Rooftop air conditioning units are known and have been used in the refrigeration industry for a considerable period. Typically a rooftop unit is either a heat pump or an air cooling unit, wherein a dividing wall separates the unit into an indoor section and an outdoor section. The indoor section receives air from the enclosure to be conditioned and discharges conditioned air back into the same area. This air is cooled or heated in a heat exchanger within the indoor section and circulated therethrough typically by a centrifugal fan. Additional heat may be supplied to increase the temperature of this air by means of electrical resistance heat, gas fired heaters or otherwise such that a single rooftop unit may meet all of the heating and cooling needs of the enclosure.
The outdoor section of the unit typically contains the compressors, outdoor heat exchanger and fans adapted to move outdoor air in heat exchange relation with the outdoor heat exchanger. If the unit is capable of reverse cycle operation, four-way valves may also be incorporated within the outdoor section.
Typically there is a closed loop vapor compression refrigeration system wherein refrigerant is increased in temperature and pressure within the compressor and then conducted to a condenser where it discharges heat to the air passing therethrough. This condensor is the indoor heat exchanger when the unit is in the heating mode of operation and the outdoor heat exchanger when the unit is in the cooling mode of operation. The condenser acts to change the state of the refrigerant from a gas to a liquid. The liquid refrigerant is then conducted through an expansion valve where its pressure is decreased such that it will evaporate, absorbing heat in the appropriate heat exchanger. This evaporating heat exchanger is the indoor heat exchanger in the cooling mode of operation and the outdoor heat exchanger in the heating mode of operation. After the liquid refrigerant has been flashed back to a gas, absorbing heat from the air in communication with the particular heat exchanger it is then conducted back to the compressor to complete the refrigeration cycle.
A rooftop type air conditioning unit is one that is typically designed to be mounted to a curb on the top of a building or structure appurtenant thereto. The unit is mounted on the roof to save valuable floor space and to provide a convenient location for service and heat transfer. Since the unit is on the roof the air from the enclosure enters and leaves the indoor section of the unit through the bottom wall of the unit and the roof of the enclosure.
With the present trend towards increasing both the seasonal energy efficiency ratio (SEER) and the coefficient of performance (COP) of air conditioning and heat pump units, it has been found advantageous to provide component arrangement within each section so as to optimize air flow per unit of energy required. Within the indoor section typically a centrifugal fan is mounted to move the indoor air through the unit and discharge same back into the enclosure to be conditioned. The energy requirements of the fan motor detract from the seasonal energy efficiency ratio and the coefficient of performance by utilizing electric energy for other than the direct transfer of heat. Particularly in the cooling mode of operation the energy input to the fan motor is critical since the fan motor is typically mounted within the indoor section and the heat generated by motor operation must be considered part of the load that the unit must cool. Consequently, any design which increases air flow per unit of energy required, results in an increased energy efficiency ratio and increased coefficient of performance. Accordingly, the energy required to produce a given amount of heating and cooling is decreased such that the operating cost to the unit and the amount of precious energy required are reduced.
Previous rooftop units have basically assembled the same components to achieve heating and cooling. It is necessary to have an intake opening to receive air from the enclosure to be conditioned, a heat exchanger to transfer heat between a refrigerant and the air, a fan to circulate the air within the unit, an optional supplemental heat source to provide heat energy to the air external of the refrigeration system and a discharge opening for conducting the air back to the enclosure to be conditioned. FIGS. 3 through 5 herein all show previous arrangements of these components within various commercial units. It can be seen that in these various arrangements the air flow path has been quite convoluted such that it has been necessary to make directional changes and otherwise operate the system with air flow inefficiencies. The herein described invention attempts to combine the components such that the angular change of direction of the air flow occurs within the centrifugal fan and such that the fan location provides for relatively straight draw through access from the heat exchanger and discharge through the supplemental heaters. The centrifugal fan is also located sufficiently far from the heat exchanger that relatively even air flow occurs such that the heat exchanger may operate efficiently over its entire surface. If the centrifugal fan were located very close to the heat exchanger, large volumes of air would be drawn through certain areas of the heat exchanger while other areas would have almost no flow at all.